An old blueprint from the early 1900s had the word "graveyard" written on the edge. No one knew it was there.

Interesting detail that dam construction destroying Mandan Hidatsa & Arikara land led to some families sending their kids to boarding school out of desperation

https://ictnews.org/news/theyre-ready-to-go-home-little-answers-offered-for-hidden-gravesite-at-catholic-mission